Those subjects w/pre-operative sarcopenia defined as the lowest quartile of the sample (standardized for height or other measures to be investigated) for thigh muscle mass estimated by magnetic resonance imaging of the thighs pre-operatively will have less post-operative physical performance improvement as revealed by change in test scores at 3- and 6-months than those who were in the highest quartile pre-operatively. Those subjects in the lowest pre-operative quartile of thigh muscle compared to those in the highest quartile will have poorer post-operative outcomes at 3- and 6-months w/respect to the following: leg extensor strength, self-reported mobility limitation, and health care resource use/complications.